Not Applicable
Not Applicable.
1. Field of the Invention
The present invention relates generally to vehicle wheel alignment systems. More specifically, the present invention relates to the identification of a target in vehicle wheel alignment systems.
2. Description of Related Art
Proper alignment of wheels in a vehicle is important for proper handling of the vehicle and proper tire wear. The alignment of a vehicle""s wheels is performed primarily by adjusting camber, caster, steering axis inclination, and toe. Other suspension problems may be detected by examining ride height and wheel offset distances. Some of these alignment measurements may also require determination of vehicle distances such as wheelbase and track width.
It is known that alignment angles may be measured by placing sensor heads on each wheel of the vehicle to form pairs that extend across the front and/or rear of the vehicle, along each side of the vehicle, and even diagonally across the vehicle. Each pair of sensor heads includes an emitter on one sensor head that, as an active target, can actively emit radiation and an image sensor at the other sensor head of the pair. The emitter is a radiating source that transmits a signal to the image sensor of the other sensor head. The image sensor converts this signal into a value that is related to alignment angle of the wheel. It is generally known to emit radiation beams in the electromagnetic spectrum at the visual or infrared wavelengths. It is also known that different types of sensors can be used in the receivers, including a linear array charged coupled device (CCD), as set forth in U.S. Pat. No. 5,489,983. It is also known that, to obtain accurate measurements, alignment systems must be able to distinguish the transmitted signal from background and scattered radiation when both are present in the signal that is received by the image sensor.
To solve the problem of background and scattered radiation, it is known for a linear CCD to capture one image when the radiating source is transmitting (on state) and to capture another image when the radiated source is not transmitting (off-state). The difference between the two images is the radiating source of interest, or the active target. Accordingly, alignment systems subtract the off-state image from the on-state image to identify the signal from the emitter. However, this on-state/off-state capture cycle for the subtraction process lengthens the time needed to conduct a vehicle wheel alignment because it necessitates the capture of two images per measurement. Additionally, the CCD image capture must be synchronized with the on-state and off-state of the radiating source. Furthermore, only one target can be identified for each on-state/off-state capture cycle, further increasing the time necessary to conduct a vehicle wheel alignment if there is a desire to identify and differentiate between multiple targets.
It is in view of the above problems that the present invention was developed. The present invention is an apparatus and method for identifying a particular target in a vehicle wheel alignment system. The vehicle wheel alignment system includes first and second units that can be attached to a pair of wheels or to a wheel and a trailer kingpin. A target containing reference points is attached to the first unit, and an image sensor containing an imaging element is attached to the second unit. The imaging element receives an image of the target and produces corresponding image data. A processor in the system identifies the image points in the image data that correspond to the reference points, and the processor calculates vehicle wheel alignment information using the image points. The reference points are preferably at least four in number and substantially collinear, having at least one known cross-ratio. The imaging element is preferably a linear CCD array that captures an image of the target, producing image data. To identify the image data corresponding to the target, the processor preferably computes a series of cross-ratios for sets of four points within the captured image and compares the cross-ratios to the known cross-ratio.
It is an advantage of the present invention to provide a target identification system in a vehicle alignment system that identifies image data corresponding to a target without using an on-state/off-state capture cycle or a subtraction process.
It is a further advantage of the present invention to provide a target identification system in a vehicle alignment system without synchronizing multiple image sensors.
It is yet another advantage of the present invention to provide a target identification system in a vehicle alignment system that identifies the target with improved accuracy.
It is still another advantage of the present invention to provide a target identification system in a vehicle alignment system that identifies multiple targets using a linear array detector with a single image capture.
Further features and advantages of the present invention will be apparent from the description below with reference to the accompanying drawings in which like numbers indicate like elements.